The present invention relates to a lamination plant, a carrier assembly for temporary accommodating solar cell laminates while conveyed through a lamination plant, a method of carrying solar cell laminates through a lamination plant and a method of transporting a carrier though a lamination plant.
Solar cells are well known in the art of energy production for producing electrical energy in an efficient and environmentally friendly way. A solar cell relies on the photovoltaic effect for generating electrical energy from visual radiation which primarily but not necessarily constitutes solar light. A typical solar cell consists of a thin silicon (Si) wafer, hereafter designated solar cell element, having a single large p-n junction applied on its upper surface which is intended to face the light. Both the upper surface and the opposite back surface of the solar cell is provided with a metal contact constituting a plus and a minus pole for generating a direct current (DC) through the solar cell element. The photons impinging on the p-n junction will excite charge carriers, which will initiate a current towards their respective poles. Solar cells may be manufactured in varying sizes and geometries.
The DC output current may be used directly for powering a facility or charging a rechargeable battery, or alternatively a rectifier may be employed to convert the DC current to an AC current, which may be delivered to a transmission grid. The above type of solar cell element yields a maximum voltage of between 0.3V-0.7V and typically 0.5V. The voltage is weakly dependent on the amount of radiation received by the solar cell. The above applications typically need to be provided with a higher voltage than the voltage delivered by a single cell. Therefore, to be able to achieve higher voltages, a plurality of solar cell elements have to be connected in series to form a solar module. Due to the very low voltage provided by each individual solar cell element, the solar modules may be manufactured including a large amount of solar cell elements. For example, in a typical commercial solar module for a nominal voltage of 60V, 144 solar cell elements may be connected in series. Typically a plurality of modules is further connected into a solar array and installed in places subjected to high solar radiation intensity.
Since the solar cell element is typically very brittle and may rupture when subjected to shocks, the solar cell elements must be encapsulated within a protective enclosure. As the solar modules are mostly located outdoors and on exposed locations such as on rooftops etc., the enclosure must be made substantially rigid. For providing improved structural strength to the solar module, the solar cell elements are typically encapsulated between two protective cover layers of substantially rigid material. The upper protective layer facing the source of solar radiation must be made of transparent material such as glass or alternatively a transparent polymeric material for allowing the solar radiation to reach the solar cell elements. The lower protective layer facing away from the source of solar radiation may be made of transparent material or alternatively a non-transparent material, i.e. an opaque material which may be reflective for allowing incoming radiation to reflect and pass the solar cell elements a second time.
The solar cell elements are permanently encapsulated between the upper layer and the lower layer to form a solar laminate. The upper and lower cover layers should have a certain thickness for giving the solar cell the rigidity required for the location where the solar laminate is to be installed. However, for reducing the weight of the solar module, the covering layers must not be too thick. A thick upper cover layer will additionally absorb a large quantity of the solar radiation, thereby making the solar module less effective. Typically, the thickness of the cover layers is in the mm range.
The upper and lower protective layers are typically permanently fixed onto the solar cell elements by an adhesive. Typically, a thin film of EVA (Ethylene-Vinyl Acetate), is used as an adhesive in the manufacturing of solar laminates. EVA film is flexible and non-adhesive at room temperature and is commercially available in the form of rolls. At a temperature of about 80° C. the EVA film melts, and at a temperature of about 130° C. the EVA film cures by polymerization. The solar cell laminate may constitute a layer of one or more solar cell elements fixed between the two protective cover layers where the film of EVA material is placed between the solar cell elements and each protective cover layer for encapsulating the layer of solar cell elements and fixing the layer of solar cell elements to the cover layers. The solar cell laminate is processed by heating for the EVA film to melt and subsequently cure. After curing the EVA film will form a solid, transparent and insulating adhesive which permanently encapsulates the solar cell elements between the cover layers.
During the heating of the solar laminate and in particular during the melting and curing of the EVA material, gas bubbles will occur within the solar laminate. The lamination process is therefore typically performed under vacuum conditions for removing any gas bubbles which may occur during heating. During processing, the solar laminate is placed on a heating plate and positioned inside a vacuum chamber under vacuum conditions. Vacuum is in the present context understood to mean a pressure significantly below ambient pressure. The heating plate is heated to a temperature of at least 80° C. for the EVA material to melt and encapsulate the solar cell elements. When the EVA material has reached liquid state, bubble evacuation is performed. During bubble evacuation gas bubbles generated inside the solar laminate by the melted EVA are allowed to escape. Additionally, an external force is applied onto the solar laminate and a certain time period is allowed to elapse for ensuring all gas bubbles dissipating into the vacuum chamber. Any gas bubbles remaining inside the solar laminate may cause incoming solar radiation to deflect. Additionally, since bubbles inside the solar laminate constitute voids, the structural stability of the solar laminate may be reduced and the insulating properties of the EVA material may be adversely affected by the bubbles.
When bubble evacuation has been performed and the EVA material is substantially bubble free, the temperature of the heating plate is increased to about 130° C. to initiate curing. The curing causes the EVA material to crosslink and thereby permanently fixes the solar cell elements to the cover layers. When the curing step is finished a permanently sealed solar module in the form of a laminate is formed. After curing, the solar laminate may be removed from the vacuum chamber and allowed to cool down to ambient temperatures.
The use of heating plates in solar applications is well known in the prior art. One example of a heating plate is found in the European patent EP 1 517 585, which discloses a heating plate having internal cavities in which a heat exchange medium and heating bodies are located. Another example may be found in the German patent application DE 10 584 034 64 describing a heating plate having at least one main heating area and at least one auxiliary heating area being heated independently from the main heating area. Yet a further example of a heating plate may be found in the German utility model DE 20 587 006 464.
Typically, the layers of the solar laminate are assembled on the heating plate outside the vacuum chamber. The layers constitute solid sheets in ambient conditions (room-temperature). The heating plate is subsequently introduced into the vacuum chamber. The current activities in the field of BIPV (Building Integrated PhotoVoltaic) have increased the demand for solar laminates having a large surface. These large surfaced solar laminates having a large active surface for receiving solar radiation are used in large solar modules/arrays and are typically mounted on buildings. Some manufacturing plants exist which produce solar laminates having an active surface of several m2. Since the solar laminates comprise glass and silicon, the weight of a single laminate may be considerable when the active area is in the m2 range. Therefore the solar laminate and the heating plate is typically conveyed on a conveying surface into the lamination plant, e.g. by the use of rollers, conveyer belts or the like. It has however been observed that the use of rollers and conveyer belts are not suitable for moving the large surfaced solar laminates, since the solar laminates are still brittle before curing and may thus easily break from shocks received during transport through the lamination plant. Such shocks are typically the result of increased friction between the conveying surface and the heating plate. Increased friction may occur when the opposing conveying surfaces are uneven. The opposing conveying surfaces are typically uneven due to manufacturing tolerances and material defects, thus shocks are difficult to eliminate. For avoiding frequent breakage of non-cured solar laminates there is a need for improved conveying and transportation devices in connection with the transport of the solar cell laminate through the lamination plant. It is therefore an object of the present invention to provide a carrier assembly suitable for both transporting and heating the solar laminates in the lamination plant.